Re: [MMUSIC] Offer/Answer PT Questions - text proposal

[Roman Shpount <[e-mail]>]

On Thu, Mar 3, 2016 at 4:51 AM, Christer Holmberg <
[e-mail]> wrote:

> >But suppose you are switched to another preexisting RTP session. It is
> new to you, but it isn't new, and has existing RTP bindings. And those
> might conflict with ones you had in your old RTP session.
> >
> >If you knew this was a new RTP session you could forget your old
> bindings, and start over.
> >
> >This sort of thing could happen if you are connecting to a conference
> server. First you are connected to an IVR to authenticate. That is your
> first RTP session. After that you are transferred into the conference.
> >That is your 2nd RTP session.
> >
> >If this is done via REFER, then you will see it as a new SIP and O/A
> session, and so will start out with an empty set of PT bindings.
> >
> >But if this is done via 3pcc, or a media relay, then we have the problem.
>
> So, then, perhaps we should allow PT re-binding within an O/A session, in
> case the underlying RTP session etc changes?
>

Yes, we should allow re-binding. This is what I was saying all along. The
only thing you need to do when re-bind PT is to change local transport or
mid so that you can decode incoming RTP packets using the right PT mapping.

To reiterate:

1. RTP session can start before the O/A session in cases of 3pcc and RTP
mixers.

2. It can continue after O/A session ends in cases 3pcc and RTP mixers

3. O/A session can migrate from one RTP session to another in case 3pcc or
RTP forwarders.

4. End point participating in O/A session does not always have access to
previous history of the RTP session it participates in and has no way to
determine when RTP session changes.

Most importantly, all of the above is irrelevant to solve the problem in
hand. Solution should be that O/A session should operate as if O/A session
is an RTP session until it encounters a conflict. If conflict is
encountered (since it is unavoidable in some architectures such as 3pcc and
RTP mixers), a recovery mechanism should be provided (allocate new local
transport and start the new RTP session).
_____________
Roman Shpount